feat: lint info on template spacing failure

Signed-off-by: Matt Butcher <matt.butcher@microsoft.com>

pkg/lint/rules/template.go

@@ -106,6 +106,7 @@ func Templates(linter *support.Linter, values map[string]interface{}, namespace
 		// chart is not compatible with v3
 		linter.RunLinterRule(support.WarningSev, path, validateNoCRDHooks(data))
 		linter.RunLinterRule(support.ErrorSev, path, validateNoReleaseTime(data))
+		linter.RunLinterRule(support.InfoSev, path, validateWhitespaceAroundTemplateDirectives(string(data)))
 
 		// We only apply the following lint rules to yaml files
 		if filepath.Ext(fileName) != ".yaml" || filepath.Ext(fileName) == ".yml" {
@@ -185,6 +186,26 @@ func validateNoReleaseTime(manifest []byte) error {
 	return nil
 }
 
+// TODO: I strongly suspect that there are better regexps than these two.
+var (
+	badTplStart = regexp.MustCompile(`{{-?[^-\s]+`)
+	badTplEnd   = regexp.MustCompile(`[^\s-]+-?}}`)
+)
+
+func validateWhitespaceAroundTemplateDirectives(template string) error {
+	badMatches := []string{}
+	if matches := badTplStart.FindAllString(template, 10); matches != nil {
+		badMatches = append(badMatches, fmt.Sprintf("\nbad start: %s", strings.Join(matches, "\n\t")))
+	}
+	if matches := badTplEnd.FindAllString(template, 10); matches != nil {
+		badMatches = append(badMatches, fmt.Sprintf("\nbad end: %s", strings.Join(matches, "\n\t")))
+	}
+	if len(badMatches) == 0 {
+		return nil
+	}
+	return fmt.Errorf("whitespace required between template markers and body: %s", strings.Join(badMatches, "\n"))
+}
+
 // K8sYamlStruct stubs a Kubernetes YAML file.
 //
 // DEPRECATED: In Helm 4, this will be made a private type, as it is for use only within

pkg/lint/rules/template_test.go

@@ -226,3 +226,31 @@ func TestStrictTemplateParsingMapError(t *testing.T) {
 		}
 	}
 }
+
+func TestValidateWhitespaceAroundTemplateDirectives(t *testing.T) {
+	for example, success := range map[string]bool{
+		"{{foo}}":                       false,
+		"{{-foo-}}":                     false,
+		"{{ foo-}}":                     false,
+		"{{ foo}}":                      false,
+		"{{-foo }}":                     false,
+		"{{foo }}":                      false,
+		"{{ foo }}":                     true,
+		"{{ default 2 .Values.foo }}":   true,
+		"{{default 2 .Values.foo }}":    false,
+		"{{ default 2 .Values.foo}}":    false,
+		`{{ default "}" .Values.foo }}`: true,
+		`{{- foo }}`:                    true,
+		`{{ legal }}{{illegal }}`:       false,
+		`{{ legal }}{{- legal -}}`:      true,
+		"{{\nlegal\n}}":                 true,
+	} {
+		if err := validateWhitespaceAroundTemplateDirectives(example); (err == nil) != success {
+			st := "failure"
+			if success {
+				st = "success"
+			}
+			t.Errorf("Expected %s for %q", st, example)
+		}
+	}
+}